> ## Documentation Index
> Fetch the complete documentation index at: https://docs.trypillow.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Participant metadata

> Every field Pillow records with an interview, the meta_ link parameters you can add, their limits, and the parameters Pillow reserves.

This page lists what an interview records about its participant: the fields Pillow captures automatically and the custom values you pass in the study link. All of them appear in the interview's **Metadata** panel. To add custom values to a link, see [Pass participant data in the link](/guides/customize-metadata).

## Fields Pillow records automatically

| Field in the **Metadata** panel | What it shows                                                                                    | Example                                    |
| ------------------------------- | ------------------------------------------------------------------------------------------------ | ------------------------------------------ |
| **Status**                      | Whether the interview is complete. See [Interviews](/concepts/interviews).                       | `Complete`, `Incomplete`                   |
| **Language**                    | The participant's language, from their browser or the link's `pillow_locale` parameter           | `French (France)`                          |
| **Location**                    | City, region, and country, looked up from the participant's IP address                           | `San Francisco, California, United States` |
| **Device**                      | The participant's operating system: `iOS`, `Android`, `macOS`, `Windows`, `ChromeOS`, or `Linux` | `iOS`                                      |
| **User agent**                  | The last part of the browser's user agent string                                                 | `Safari/604.1`                             |

A field Pillow can't determine shows `Unknown`.

## Custom parameters

Any link parameter that starts with `meta_` is saved as a custom field. Pillow removes the prefix and keeps the rest of the key as you typed it, so `meta_user_id=usr_48213` becomes `user_id` with the value `usr_48213`. The prefix is not case-sensitive: `META_source` also works.

| Rule                                | Limit                                                                                                  | What happens past the limit                                         |
| ----------------------------------- | ------------------------------------------------------------------------------------------------------ | ------------------------------------------------------------------- |
| Characters in a key (after `meta_`) | Letters, numbers, `_`, `.`, `-`                                                                        | The parameter is dropped.                                           |
| Key length                          | 64 characters                                                                                          | The parameter is dropped.                                           |
| Value length                        | 512 characters                                                                                         | The value is cut at 512 characters.                                 |
| Number of parameters                | 50                                                                                                     | The earliest parameters in the link are dropped until 50 remain.    |
| Total size                          | 2,048 characters for all keys and values, counting the quotes and separators added when they're stored | The earliest parameters in the link are dropped until the rest fit. |

Values are stored as text. If a key appears twice, the last value wins.

## When metadata is captured

* Metadata is saved once, when the participant starts the interview. It can't be edited afterwards.
* A participant who reopens the link in the same browser within 30 days returns to their existing interview, which keeps the metadata from their first visit, whatever parameters the second link carries.

## Other link parameters

`pillow_locale` sets the interview language, for example `pillow_locale=fr-FR`. See [Supported languages](/reference/languages).

Parameters that start with `dp_` or `pillow_` are reserved for Pillow. Use `meta_` for your own data.